Cells may interact directly through molecules expressed at the cell surface or via diffusible messengers in the form of neurotransmitters, hormones and growth factors. These interactions are crucial for the establishment of order during development, for sensory perception, behavioral responses and for maintenance of the physiological state. Aberrant cellular communication has been largely studied in mammals in situations where it leads to inappropriate cell growth, contributing to neoplasia. In invertebrates such as Drosophila and C. elegans, it has also been possible to use genetics to study specific disruptions in developmental and behavioral pathways. It seems likely that many principles of cellular interaction will be universal in eukaryotes. There is already evidence that at least one class of molecule, the protein kinases, are required for specific behaviors and developmental decisions and when altered can lead to neoplasia. A large class of extracellular signalling molecules stimulate the synthesis of cAMP in target cells, thus activating the cAMP-dependent protein kinase (PKA) and effecting the appropriate response, initially by the phosphorylation of intracellular proteins. The objective of this research proposal is to define the biological roles of PKA in a whole organism, Drosophila. Particular pathways of cellular communication that use PKA will be investigated further with the techniques of genetics and molecular biology to characterize the biological decision or information being transmitted between cells and the molecular pathway of its execution. Genes for components of Drosophila PKA have been cloned and have been used to generate null mutations and dominantly acting mutant genes that lead to alterations in PKA activity in vivo. The phenotypic consequences of these mutations have shown that PKA is essential to the viability of fertility of Drosophila but is not necessary for the growth and viability of individual cells. Specifically, the kinase is required for normal patterning of Drosophila embryos and is essential for maintaining the normal structural organization of the egg-chamber during oogenesis. Further studies will seek to resolve the different roles of PKA in embryogenesis and to determine how phosphorylations in oogenesis lead to alterations in cytoskeletal architecture. A major objective is to isolate genes that collaborate with PKA in these biologically important pathways of signal transduction. This will be accomplished by the isolation of genetic modifiers of PKA-associated mutant phenotypes and by direct biochemical testing of candidate substrates of PKA. These studies are the first to investigate systematically the functions of cAMP-mediated signal transduction in a metazoan. They will yield information about normal regulatory interactions that are mediated by cAMP during development that will be applicable to the study of human birth defects and those human malignancies that have been shown to involve deregulation of normal cAMP signalling.